Throttle Position Sensor

[saintnick]

On the carbed mk1s, does removal of TPS help smooth out low down fuelling? Someone mentioned this to me, I have no idea whether or not its complete bollox. I associate the TPS with FI - I know that the throttle sensor has played a part in aggrevating fuelling on some KTMs, for example, and the SV is a bit snatchy at low revs for a carbed bike. The jetting itself is pretty good, we had her on a mate's dyno and apart from running a tad lean coming off idle, fuelling was pretty much spot on (68 bhp at wheel). Which made me wonder about the TPS.

[Sid Squid]

Throttle position is a good indicator of engine load, as such the TPS is effectively a load sensor, it's connected to the ignition system and the ECU will alter timing slightly to account for load.

Checking its setting is worthwhile if you think throttle transitions are not as smooth as they should be, but in my experience such problems are most commonly carburation.

[saintnick]

this (http://forums.sv650.org/showthread.php?t=55459) was interesting....

Because of the AF mix on the dyno print out, I'm fairly sure that it is a TPS issue rather than the carbs, we shall see.

[Sid Squid]

Do you have setup figures for the sensor?

[saintnick]

Do you have setup figures for the sensor?

Nope, only figures I have are from the dyno, runs were done with TPS in situ which as far as I know is in standard trim.

Looking at that thread, I reckon that disconnecting a TPS on a carbed bike would simply leave the ignition at max advance and thus have no negative implications. FI bikes may respond differently to bypassing the sensor since FI and a TPS work hand in hand (in theory). That's why I was surprised to find that carbed SVs employed a TPS in the first place: not many carbed bikes did.

It's an interesting one because some carbed SVs are a little unusual in that they can be jumpy when bringing power in, say exiting a bend, and that is something I associate more with FI. Since the fuelling seems to be OK, its probably worth while disconnecting and seeing what happens. Unfortunately the pix in the thread relate to the FI model which presumably is different in the connector department, if anyone has bypassed on a carbed bike, I'd be interested in where you unplugged the thing.:)

[Sid Squid]

Looking at that thread, I reckon that disconnecting a TPS on a carbed bike would simply leave the ignition at max advance and thus have no negative implications.
Could be - I've never measured that, but as for no negative implications, I disagree, as said it's essentially a load sensor - there's no question it will run without the sensor/sensor set wrong, but it's definately better with it set correctly, it's not the difference of pulling a plug lead off, but there is a difference.
FI bikes may respond differently to bypassing the sensor since FI and a TPS work hand in hand (in theory).FI system work very differently - but the TPS is still a load sensor in the same way - of course it also does other things too.
That's why I was surprised to find that carbed SVs employed a TPS in the first place: not many carbed bikes did.
Many late carb bikes of my knowledge do, mostly from the mid 90s forward.
It's an interesting one because some carbed SVs are a little unusual in that they can be jumpy when bringing power in, say exiting a bend
This is why - not withstanding your obvious careful attention to the carburation - I'm thinking that something else is possibly the problem, SVs are neither notably smooth or notably rough, by what measure do you feel that the bike is not right? I appreciate this is difficult to express in a forum post.
If anyone has bypassed on a carbed bike, I'd be interested in where you unplugged the thing.:)If you wished it disconnected then at the sensor is as good as anywhere else.

TPS setup, (from Suzuki's own workshop manual):

Looking at the end of the connector you will see it is roughly heart shaped, there are three pins, two next to each other at the wide end, and one at the narrow end, call the the single pin at the narrow end 'A' and the upper left hand one 'B' and the right hand one 'C'

Throttle shut - 3.5 - 6.5 K-ohms between 'A' and 'B'
Throttle open - Resistance between pins 'A' and 'C' should be 78% of the resistance of the resistance between 'A' and 'B'.

[saintnick]

Cheers for that, especially the last bit, I reckon the only solution is to sse what happens. The old SV - which was an ex minitwins JHS bike - had no throttle position sensor and from memory is what a lot smoother getting on the throttle low down. That's how best to desscribe what I'm feeling, getting on the gas from a closed throttle the bike reminds of a 990 Superduke.... or in fact lots of FI KTMS... all or nothing stylee.

It does seem that the thread on this subject had people reporting similar findings, and remedied by ditching (or by passing) the tps.

[embee]

As said, the TPS on the carbed engine is a part load ignition advance device, just like the vacuum advance capsule on old distributors. My SK1 has it.

The engine needs more ign adv at part load to achieve the best combustion (economy). It's well worth setting it up correctly. There is no advantage in deleting it, it's lose/lose, it won't run as well at light load and will give worse economy.

As said, the most likely candidate for poor off idle running is carb adjustment. Balancing the carbs for vacuum is easy, adjusting the idle mixture on a running SV engine is more tricky due to where the adjuster screws are situated. They really need to be set while the engine is running to allow for variations in manufacture (jet sizes etc)

There are special angled-drive tools like this example (http://www.pvrdirect.co.uk/productinfo.aspx?catref=VS0530), but they tend to be expensive.

I have managed it with a thin thermal glove and a short screwdriver, I can just get my hand through the frame gap but it's tricky and you need to know where the adjusters are by feel because you're working blind. People often find the screws are corroded and won't move, so the carbs need to come off for cleaning anyway.

US bikes had anti-tamper plugs fitted to the screws.


Also double check the choke cables and plungers are free, stuck plungers will ruin light load running when warm.

[saintnick]

Interesting.

Are you sure the TPS wasn't emissions related rather than economy related?

It could be that coming of idle it needs a tweak, one reason why I thought the problem was TPS related was because members reported this problem and suggested TPS removal as remedy in that thread (http://forums.sv650.org/showthread.php?t=55459).

Unfortunately dyno runs are buch better at showing you what's happening when you're on the throttle where everything looked good, so the dyno charts don't really help. Ta to both of you for the info.

[saintnick]

Done some research. Yup, late 90s carbed bikes did use them like you suspected, and yup - they are strictly emissions related. What they do is retard the ignition at part throttle low down the range , because that is where the emissions legislation was severe.

My other bike (carbed) had a TPS, which was disconnected by the tuner. (The cdi reverts to default, ie an open throttle map = optimum advance throughout.) Since I ended up with 130 brake at the wheel as opposed to 90 I don't think the bike misses it, although obviously there are other mods :D

With FI, the TPS can do more sophisticated stuff, but the TPS on the SV just retards the ignition until revs are out of the emission zone - if its anything like the Kwak K-Trick system. This may be wrong, but looking at bikes of a similar vintage, that does seem to be the story. Proof of pudding will be in eating, but I am bearing in mind that there may be other issues.

[Sid Squid]

they are strictly emissions related
I sincerely doubt this. Timing - at least for best torque at part throttle - must take account of load, historically was done by vacuum, (as Embee rightly points out), the modern equilavent is throttle position sensing.

[saintnick]

sid, not sure what you doubt. :)

that its was originally put there for emissions?

or that bikes with the tps by-passed wont run as well as those with? some members on here would appear disagree with that, on the basis of their experience reported on the old TPS thread.

all it does - at least on carbed bikes like the zrx - is retard ignition timing at specific revs. I completely agree that regarding the SV, I can't be certain what the result of a bypass would be, that's why I was asking, but based on other machines it seems likely that its absence would merely result in a default CDI setting, and why that default setting would not be to run all revs at optimum advance seems hard to fathom.

What I suspect is that in effect the TPS improves fuel consumption / emissions but compromises performance up to a certain point in the range.

Kawasaki actually issued a ZRX map - in fact its a 3d graph with 3 axis ie revs, degree of timing, and percentage of throttle opening - to show how their TPS kicks in, I have a link if interested.

Thing is, a strict interpretation of embees post would mean no carbed bike without a TPS could run as well as one with, something which tuners all over the world would take issue with. If ignition is set to optimum advance, it will do the job irrespective of load, although it may not be as fuel efficient as a TPS bike - which brings us back to emissions. Anyway, always good to have input irrespective of outcome, including me being wrong, and I appreciate that.

[Sid Squid]

sid, not sure what you doubt. :)

that its was originally put there for emissions?
Yes, it's not an emission control device.

is retard ignition timing at specific revs.
No, it affects timing by taking account of engine load - which throttle position is a good indicator of.

but based on other machines it seems likely that its absence would merely result in a default CDI setting, and why that default setting would not be to run all revs at optimum advance seems hard to fathom.
Optimum timing is not decided solely by engine speed, load is very important, that's what the TPS takes account of, obviously on a carbed bike it can only affect timing, FI bikes are different of course, but guess what? Primary function of TPS on those bikes is load indication. SV ignition is not CDI.

What I suspect is that in effect the TPS improves fuel consumption/emissions but compromises performance up to a certain point in the range.
It may affect consumption at part throttle - but that's an effect of correct timing taking account of load, rather than a specific 'economy' function.
Emmisions and economy are not the same thing - you can burn a small amount of fuel badly, and by the same token you can burn a large amount of fuel very well.

Thing is, a strict interpretation of embees post would mean no carbed bike without a TPS could run as well as one with, something which tuners all over the world would take issue with.
Embee works in engine development and his knowledge of this stuff is a quantum leap ahead of ours. I don't doubt that many tuners take little account of part throttle running - WOT is ordinarily what everything is tuned to, and that's an area where TPS will have least, (if any), effect. Any carbed engine will run without the TPS - but part throttle running will not have best ignition timing.
If ignition is set to optimum advance, it will do the job irrespective of load.
Which assumes there is one 'optimum', that suits all throttle positions, cylinder conditions dictate otherwise. There may be one setting which is fine for WOT based solely on engine speed, but this won't be the 'optimum' at other throttle openings.

although it may not be as fuel efficient as a TPS bike - which brings us back to emissions.See my comment above about emissions/economy.
Anyway, always good to have input irrespective of outcome, including me being wrong, and I appreciate that.
There's only one person who habitually contributes in here who really really knows the detail of such things - Embee, not me that's for sure! :D

All said if you were constructing a bike for racing which didn't have a TPS there'd be little benefit in the bother of getting and setting up one, WOT is really all you'd be concentrating on, and as said above that's an area where the TPS has its least, if any, effect. But if you're constructing one. like an SV, that already has one there's no benefit in removing it - if it's working right that is, if not then by all means bin it. But there will be a negative effect, it may be an irrelevant effect if you're running a race bike where part throttle running isn't what you're concentrating on, but there will be an effect.

[saintnick]

Ta for that.

I think there maybe some confusion here between how the device works (no arguments from me on that score) and what it does in reality, which is where we part company. I think its functionality is limited, as previously described. At some point I'll try life without it for a while and report back, since a practical evaluation is the only answer - some members have already done this and reported their findings, which seem to be consistent with low rev retarding. I still maintain that the device would not be there if there was no emissions legislation: this (http://www.picoauto.com/tutorials/emissions-components-actuators.html) is just one of many references.

CDI: call it an ECU if you prefer, but the SV clearly does have an Ignitor which I assume is a conventional CDI unit. The SV service manual refers to it as a Digital Ignitor. There are certainly plenty of threads referring to it as a CDI on here.

[embee]

Steady on there. Sid ;)

I guess what is being referred to is an ignition map, something like
http://www.btinternet.com/~triumph/renault_ignition_map.jpg

What you see on the "front-right" face at around 1000mBar is the "full load" ignition advance curve. That's what traditional (i.e. old fashioned) bike engines ran with. It would be approximated with centrifugal weights and spring devices which could give perhaps 3 slopes versus speed, or fixed/slope/fixed type relationships.
That would often allow a reasonable fit to the "optimum" ignition requirement for best torque at any speed with Wide Open Throttle (WOT).

Car engines, where fuel economy was a more important consideration, were fitted with a vacuum sensing system to provide the extra advance needed in order to fit the other axis, the "load" or throttle opening at a given speed. A very convenient measure for this is the inlet manifold absolute pressure (MAP), and originally a vacuum capsule was used which pulled the points backplate round as the manifold vacuum increased at small throttle opening, thus advancing the ignition timing. This was traditionally considered an un-necessary complication for bike engines where no-one really cared much about fuel economy or part load running.

Yes an engine will run on just a full load function, but it's wasting a lot of potential benefits.

Light load needs more ignition advance because the burn is slower than at full load, the charge density is lower and generally charge motion is less, so flame speed reduces. Combustion can be considered in simple terms as 3 phases, the initiation where the spark gets a kernel of flame going (the first 5 or 10% of the total mass of charge), the main phase (10-90%), and the end phase (last 10%). It isn't a simple relationship because the 3 phases don't all respond to speed/load in the same way, but generally speaking light load (or EGR dilution, or weak mixtures) needs more advance becasue of slower flame speeds and slower initiation of burn.

The mechanical systems were superceded by electronic systems, with programmed values for ignition advance against speed (using triggers) and load (often inlet MAP). MAP sensors work quite well with multi-cylinder manifolds, but for individual port runners (as on bikes) this gets less convenient due to pulsing, and correlating load to throttle position against speed enables a decent measure of load to be achieved. Note that "full load" is achieved at quite small throttle openings at low speed but wider openings as speed increases, so it has to be "mapped" against speed. Many cars use a "mass flow sensor" (principally for fuelling but also giving a load measure), which have significant advantages over both TPS and MAP sensing, but cost more and need careful installation conditions.

I suspect what might be interpreted as "retarding the ignition" is the fact that an ECU can only calculate angle after a trigger point, it can't anticipate it, so all ignition calculations are a retard after a trigger point, more retard at full load, less at light load. Ignition trigger wheels or pulses often consist of a number of even pulses and an odd one, or something equivalent, so it can work out angular position and speed and then fire the ignition for each cylinder at appropriate times. The crank angle reference might be say 60deg BTDC, so all ignition values are retarded from that.

Ignition advance does have an effect on emissions (HC/CO/NOx) and modern car engines use it to considerable effect, particularly when controlling NOx production, but I rather doubt it was used much for that reason on the last generation carb bike engines (don't know for sure, haven't been involved in the OE engineering of bike engines). Regulated emissions at that time weren't particularly demanding for bikes, and the shortcomings of carbs far outweigh the effects achievable with a few degrees of ignition. If anyone knows different for definite it'd be an interesting topic.

HTH

[Sid Squid]

See what I mean :D, Embee knows this stuff rather well!

CDI is something quite specific; capacitor discharge ignition. CDI doesn't mean computerised digital ignition or any of the other various things that I've heard corrupted from CDI. It's been written here on this very site approximately 78,000,000 times that SVs have CDI, that's still wrong though :D.

As a brief and almost criminally simplified explanation I wrote this. (http://forums.sv650.org/showpost.php?p=926191&postcount=11)

[saintnick]

Excellent info from contributors, and yup, I did know it was capacitor discharge....

There is no doubt that TPS usage has evolved massively - these days it seems to be involved in everything from kickdowns to traction control (and BMW anti knock systems). But even in early SV days some territories - like California - already had emissions legislation, and we were gearing up for the notorious Euro 3 directive. When you think about it quite a few emissions related bits and bobs had already appeared on bikes by the end of the nineties: ie air going back into the bike's zorst, header design, and.... the TPS. Cats were next.

I worked on a dyno for a while, and I recall that while carbed bikes with an aftermarket ignition advancer did benefit slightly by comparison with same model bikes and OE ignition set up, setting the carbs up and optimising jetting for a decent A/F mixture through the range was by far the most important step. Carbs still have their fans, getting FI spot on for bikes has taken an awful lot of time, to the extent that riding with some decent well set up carbs can still surprise, crisp but oh so smooth...
these Mikuni TMRs are nice, a favourite on big retros for road and race:

http://i301.photobucket.com/albums/nn69/750cc/tmr4.jpg

I've ridden some horrendously set up standard FI bikes: Fazers from a couple of years back, many KTMs - early 990 superdukes come to mind at once ;), Honda SP1 etc. In general though, bike FI is by and large sorted. It is 2011, after all....

Ironically, it was because the Sv seemed a bit snatchy in an iffy FI way coming from a closed throttle that the thread started, and I haven't ruled out the possibility that the carbs are at the bottom of the issue.

[johnnyrod]

Goign back to something on page 1, Nick reckoned that removing the TPS would give most ignition advance. Add this to the fact it's an ex-JHS bike and they (at least used to) sell ignition advance Woodruff keys, I would reckon the smoother/better bottom end comes from ignition advance which adds a good jollop of bottom end torque while making almost no difference to the top end (so ideal for a Minitwin where bhp is the defining thing).